ABSTRACT

Objective:

Marijuana is the most widely used illegal substance in the world. The target analyte for cannabinoids analysis in urine is THCCOOH. The most widely used sample preparation methods for THCCOOH are liquid-liquid extraction (LLE) and solid phase extraction (SPE). The aim of this work is to compare the extraction methods (LLE and SPE) for (±)-11-nor-9-carboxy-Δ9-THC (THC-COOH) for synthetic urine samples (n=80) prior to Gas Chromatography Mass Spectrometry (GC-MS) analysis. In addition, a method validation was conducted in terms of reproducibility, selectivity, accuracy, precision and linearity.

Materials and Methods:

(±) -11-nor-9-carboxy-Δ -THC and (±) - 11-nor-9-carboxy-Δ9-THC-D (as the internal standard) were used in the 3 studies. Toxi tube B and Clean Screen THC cartridges were used for LLE and SPE, respectively. BSTFA with 1% TMCS were used in the derivatization step. The analysis is performed with Thermo Finnigan Trace GC-MS. Minitab11 was used in statistical evaluations.

Results:

The limit of detection (LOD) was found to be 2 μg/L. All recovery values were >90% with RSD values <10%. A calibration curve for the standard stock solutions of 25-500 μg/L was obtained with a coefficient of variation (R2) of 0.9968 which indicates a good linearity. The Anderson-Darling test applied indicated that, LLE and SPE results do not follow a normal distribution, therefore, a non-parametric test, Wilcoxon signed-rank test was used in statistical evaluations.

Conclusions:

The linearity, repeatability and recovery values obtained in the study were found to be in accordance with bioanalytical validation criteria. According to the statistical results obtained, a significant difference between LLE and SPE was found (p <0.005). By means of this study, the importance of sample preparation steps prior to analysis has been shown.